Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as an energy source for electric vehicles and hybrid electric vehicles, which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel. As a result, kinds of applications using the secondary battery are being increased owing to advantages of the secondary battery, and hereafter the secondary battery is expected to be applied to more applications and products than now.
As kinds of applications and products, to which the secondary battery is applicable, are increased, kinds of batteries are also increased such that the batteries can provide outputs and capacities corresponding to the various applications and products. Furthermore, there is a strong need to reduce the sizes and weights of the batteries applied to the corresponding applications and products.
Small-sized mobile devices, such as mobile phones, personal digital assistants (PDAs), digital cameras, and laptop computers, use one or several small-sized, light battery cells for each device according to the reduction in size and weight of the corresponding products. On the other hand, middle- or large-sized devices, such as electric bicycles, electric motorcycles, electric vehicles, and hybrid electric vehicles, use a middle- or large-sized battery module (or a middle- or large-sized battery pack) having a plurality of battery cells electrically connected with each other because high output and large capacity is necessary for the middle- or large-sized devices. The size and weight of the battery module is directly related to the receiving space and output of the corresponding middle- or large-sized device. For this reason, manufacturers are trying to manufacture small-sized, light battery modules. Furthermore, devices, which are subject to a large number of external impacts and vibrations, such as electric bicycles and electric vehicles, require stable electrical connection and physical coupling between components constituting the battery module. In addition, a plurality of battery cells are used to accomplish high output and large capacity, and therefore, the safety of the battery module is regarded as important.
Based on their shapes, secondary batteries used as unit cells for such a battery module or battery pack are generally classified into a cylindrical battery, a prismatic battery, and a pouch-shaped battery. Among them, the pouch-shaped battery has attracted considerable attention since the pouch-shaped battery can be stacked with high integration, has high energy density per unit weight, is inexpensive, and can be easily modified.
The pouch-shaped battery is a battery constructed in a structure in which an electrode assembly having a cathode/separator/anode structure is mounted in a pouch-shaped battery case made of, for example, an aluminum laminate sheet while the electrode assembly is impregnated with an electrolyte in a sealed state. A representative example of the pouch-shaped battery may be a lithium-ion polymer battery (LiPB). The LiPB is a battery constructed in a structure in which cathodes, anodes, separators are joined with each other, while the separators are disposed respectively between cathodes and anodes, and the joined cathodes, anodes, and separators are impregnated with a lithium electrolyte, thereby maximally preventing the leakage of the electrolyte. Generally, the electrode assembly is manufactured by coating adhesive layers to opposite sides of the respective separators, and thermally welding the cathodes and anodes, to which active materials are applied, to the corresponding separators.
FIG. 1 typically illustrates a general structure of a representative LiPB including a stacking type electrode assembly.
Referring to FIG. 1, the LiPB 100 is constructed in a structure in which an electrode assembly 120 including cathodes, anodes, and separators disposed respectively between the cathodes and the anodes is mounted in a pouch-shaped battery case 110 in a sealed state such that two electrode leads 130 and 140 electrically connected to cathode and anode taps 122 and 124 of the electrode assembly 120 are exposed to the outside of the battery case 110.
The battery case 110 is made of a soft wrapping material, such as an aluminum laminate sheet. The battery case 110 includes a case body 112 having a hollow receiving part 111 for receiving the electrode assembly 120 and a cover 113 integrally connected to the case body 112.
The electrode assembly 120 of the LiPB 100 may be constructed in a jelly-roll type structure in addition to the stacking type structure shown in FIG. 1. The stacking type electrode assembly 120 is constructed in a structure in which the cathode taps 122 and the anode taps 124 are welded to the electrode leads 130 and 140, respectively, and insulation films 150 are attached to the upper and lower surfaces of the electrode leads 130 and 140 for securing electrical insulation and sealability between the electrode leads 130 and 140 and the battery case 110.
The LiPB 100 manufactured as described above is shown in FIG. 2. For convenience of description, the LiPB will be referred to as a battery cell.
Referring to FIG. 2, when the battery case 110 is thermally welded while the electrode assembly (not shown) is mounted in the battery case 110, sealing parts 114 and 115 are formed at the upper end and opposite sides of the battery case 110. Among them, the side sealing parts 115 are vertically bent upward such that the side sealing parts 115 are brought into tight contact with the battery cell body 116, whereby the total size of the battery case 110 is decreased. On the other hand, the upper-end sealing part 114 is not bent because the electrode leads 130 and 140 protrude from the battery case 110 through upper-end sealing part 114.
A middle- or large-sized battery module using the battery cell may be constructed in various manners. For example, one to four battery cells may be mounted in an additional member, such as a cartridge, and a plurality of cartridges may be stacked such that the cartridges are electrically connected with each other. Alternatively, a plurality of battery cells are stacked, without using additional cartridges, such that the battery cells are electrically connected with each other. The former example has an advantage in that the battery module has a structural stability but has a disadvantage in that the manufacturing costs of the battery module are high, and the size of the battery module is big. The latter example has an advantage and disadvantage directly opposite to the former example.
However, the battery cell shown in FIG. 2 has a low mechanical strength although the battery module is constructed in any structure. As a result, the battery module has a disadvantage in that the battery module including the battery cell is weak to external impacts. Especially, the upper end of the battery cell, including the electrode leads (the electrode terminals) and the sealing parts, which is indicated by a dotted-line region A of FIG. 2, is weak to dropping or external impacts. For example, the electrode terminals are connected to additional connecting members for electrical connection. When the battery cell moved toward the electrode terminals due to the dropping of the battery module or application of external impacts to the battery module, the battery cell body may be brought into contact with the connecting members or coupling members with the result that the battery case may easily break. Also, a short circuit may easily occur due to the contact between the battery cell body and the electrode terminals or the connecting members.
Consequently, there is high necessity for a measure to effectively solve the above-mentioned problems.